Picture two buyers walking into the same lender on the same day, financing the same $350,000 house with 5% down. One has a 780 credit score. The other has a 630. They'll get quoted from the same rate sheet, insured by the same PMI companies, and shop the same home insurance market. What they will not get is the same monthly payment.
The reality is that bad credit doesn't cost you once. It costs you on three separate lines of the same mortgage, and most buyers only find out about the first one.
The first cost: your rate isn't just your rate
When Fannie Mae or Freddie Mac buys your loan, they charge the lender a fee based on your credit score and your loan-to-value ratio. It's called a loan-level price adjustment, or LLPA. The lender doesn't absorb that fee. They build it into your rate.
Here's what that actually looks like on paper. At 95% financing, a borrower with a 780+ score is charged an LLPA of 0.25% discount points. A borrower at 639 or below is charged 2.25% discount points. That's a two-point spread in upfront pricing, and using the rough industry conversion of about four LLPA points to one rate point, it works out to roughly half a percentage point of rate difference. Not because the market moved. Because of one number on a credit report.
Freddie Mac's Primary Mortgage Market Survey has the 30-year fixed rate averaging 6.67% this week, which reflects borrowers with strong credit and 20% down. On our $332,500 loan, half a point of rate difference is about $111 more per month, or roughly $13,350 over the first ten years. That's before either buyer has touched PMI or insurance.
The second cost: your mortgage insurance is priced the same way
PMI exists because the buyer put down less than 20%. It protects the lender if the loan defaults, not the borrower. What most people don't realize is that PMI on a conventional loan isn't a flat rate either. It's tiered by credit score, the same way the rate is.
A borrower at 760 or above can pay as little as roughly 0.46% annually. A borrower with a weaker score can pay well over 1% on the same coverage, the same loan, the same house. On our example loan, that gap runs over $200 a month. Same policy. Same lender. Different price, because of the same three-digit number that already hit the rate.
The third cost most buyers never connect to credit at all
This is the one that catches people off guard, because it has nothing to do with the mortgage. In most states, home insurers price your premium partly using a credit-based insurance score, a separate calculation from your FICO score, run by the insurance company rather than the lender. Research from the National Bureau of Economic Research found that homeowners with weaker credit pay meaningfully more, on average around 24% more, than homeowners with strong credit for identical coverage.
On a policy running close to the national average of roughly $2,500 a year, that gap adds up to around $50 a month. It's a smaller number than the first two, but it's stacking on top of them, and almost nobody budgets for it because they don't think of insurance as a credit product.
I'll add the caveat here because it matters: this isn't universal. California, Massachusetts, and Maryland currently bar insurers from using credit history to price homeowners insurance at all. Everywhere else, it's part of the calculation.
What it actually adds up to
Same house. Same lender. Same closing day. The only variable is credit score, and it adds up to roughly $380 more per month for the buyer with the weaker score, which is close to $46,000 over the first ten years of the loan. That's not a rounding error. That's a car, or a year of daycare, or a real dent in retirement savings, depending on where the buyer chooses to feel it.
I want to be clear about what this is not. It's not a lecture about credit responsibility. Buyers end up with lower scores for all kinds of reasons that have nothing to do with financial discipline. What it is is a math problem that almost nobody sees coming, because lenders quote a rate and a payment, not a three-line breakdown of why that payment is what it is.
What actually moves the number
Chasing a 780 isn't a realistic goal for most buyers in this position, and it doesn't need to be. The LLPA tables move in roughly 20-point bands. Climbing out of the bottom tier into the next one, or out of the high 600s into the low 700s, drops the LLPA and often the PMI tier at the same time. That's the more useful target than an abstract "perfect credit" number, because it's reachable in months, not years, and it moves real dollars off the payment.
If you're getting ready to buy and want to see where your own numbers actually land on these tables, that's worth a real conversation before you're staring at a loan estimate wondering why the payment looks different than you expected.